Passover was instituted the evening preceding the Exodus from Egypt. The first Passover was observed about the time of full moon, on the 14th day of Abib (later called Nisan) in the year 1513 B.C.E.
This was thereafter to be celebrated annually. (Ex 12:17-20, 24-27) Abib (Nisan) falls within the months March-April of the Gregorian calendar. Passover was followed by seven days of the Festival of Unfermented Cakes, Nisan 15-21. Passover commemorates the deliverance of the Israelites from Egypt and the ‘passing over’ of their firstborn when Yahweh destroyed the firstborn of Egypt. Seasonally, it fell at the beginning of the barley harvest.—Ex 12:14, 24-47; Le 23:10. Supplemental: Questions as to Time Order: It was a question of defilement that gave rise to the words: “They themselves did not enter into the governor’s palace, that they might not get defiled but might eat the passover.” (Joh 18:28) These Jews considered it a defilement to enter into a Gentile dwelling. (Ac 10:28) This statement was made, however, “early in the day,” hence after the Passover meal had taken place. It is to be noted that at this time the entire period, including Passover day and the Festival of Unfermented Cakes that followed, was at times referred to as “Passover.” In the light of this fact, Alfred Edersheim offers the following explanation: A voluntary peace offering was made on Passover and another, a compulsory one, on the next day, Nisan 15, the first day of the Festival of Unfermented Cakes. It was this second offering that the Jews were afraid they might not be able to eat if they contracted defilement in the judgment hall of Pilate.—The Temple, 1874, pp. 186, 187. “The first day of the unfermented cakes.” A question also arises in connection with the statement at Matthew 26:17: “On the first day of the unfermented cakes the disciples came up to Jesus, saying: ‘Where do you want us to prepare for you to eat the passover?'” The expression “the first day” here could be rendered “the day before.” Concerning the use of the Greek word here translated “first,” a footnote on Matthew 26:17 says: “Or, ‘On the day before.’ This rendering of the Gr. word [pro´tos] followed by the genitive case of the next word agrees with the sense and rendering of a like construction in Joh 1:15, 30, namely, ‘he existed before [pro´tos] me.'” According to Liddell and Scott’s Greek-English Lexicon, “[pro´tos] is sts. [sometimes] used where we should expect [pro´te·ros (meaning ‘former, earlier’)].” (Revised by H. Jones, Oxford, 1968, p. 1535) At this time, Passover day had come to be generally considered as the first day of the Festival of Unfermented Cakes. So, then, the original Greek, harmonized with Jewish custom, allows for the question to have been asked of Jesus on the day before Passover. “Preparation.” At John 19:14, the apostle John, in the midst of his description of the final part of Jesus’ trial before Pilate, says: “Now it was preparation of the passover; it was about the sixth hour [of the daytime, between 11:00 a.m. and noon].” This, of course, was after the time of the Passover meal, which had been eaten the night before. Similar expressions are found at verses 31 and 42. Here the Greek word pa·ra·skeu·e´ is translated “preparation.” This word seems to mark, not the day preceding Nisan 14, but the day preceding the weekly Sabbath, which, in this instance, was “a great one,” namely, not only a Sabbath by virtue of being Nisan 15, the first day of the actual Festival of Unfermented Cakes, but also a weekly Sabbath. This is understandable, since, as already stated, “Passover” was sometimes used to refer to the entire festival.—Joh 19:31. Time of his death: The death of Jesus Christ took place in the spring, on the Passover Day, Nisan (or Abib) 14, according to the Jewish calendar. (Mt 26:2; Joh 13:1-3; Ex 12:1-6; 13:4) That year the Passover occurred on the sixth day of the week (counted by the Jews as from sundown on Thursday to sundown on Friday). This is evident from John 19:31, which shows that the following day was”a great” sabbath. The day after Passover was always a sabbath, no matter on what day of the week it came. (Le 23:5-7) But when this special Sabbath coincided with the regular Sabbath (the seventh day of the week), it became “a great one.” So Jesus’ death took place on Friday, Nisan 14, by about 3:00 p.m.—Lu 23:44-46.